One type of jet engine typically used on large commercial airliners is a turbofan jet engine. Such turbofan engines have a compressor, combustor and turbine, and include a fan mounted on the front of the engine. These fans, some as large as 10 feet in diameter, draw air into the engine. Some of the air is sent to the compressor and the combustor, while the rest bypasses these components through ducts along the outside of the engine. The fans include fan blades that rotate at speeds up to approximately 9,000 rpm during operation of the engine and are enclosed in a fan housing that radially surrounds the fan. Turbofan engines for airliners typically include a nacelle that at least partially surrounds the engine and provides an aerodynamic shell to minimize drag. Typical nacelles generally comprise an inlet assembly located in front of the fan, generally being attached to the fan housing and shaped to direct air into the engine, a fan cowl that encloses the fan, and a thrust reverser adjacent the rear part of the engine.
The inlet assemblies for turbofan jet engine nacelles typically include an inner barrel, an outer barrel, a forward bulkhead, and an aft bulkhead which spans between the inner and outer barrel. Typically, the aft bulkhead is an annular metal plate that is designed to fracture during the initial (albeit extremely unlikely) impact of a fan blade-out event or during the subsequent loads from the windmilling effect of the unbalanced fan. During a fan blade-out event, the fan blade impacts the fan housing at a high rate of speed generating a large impact force that is transmitted from the fan housing to the inlet assembly attached to the housing. After a fan blade-out event, the engine is shut down but the fan can continues to rotate or “windmill” as the plane is flown to a destination for repair. However, the fan is generally unbalanced and thus continued rotation of the fan can cause high loads on the fan housing. The bulkhead thus generally is reinforced with a series of structural support members extending between the inner barrel and outer barrel and connected to the bulkhead at spaced apart locations. In existing designs, the support members are spaced such that the inlet remains intact with the bulkhead being held together by the support members. The use of structural support members on the aft bulkheads of prior art inlet assemblies, however, increases the weight and cost of the nacelle.
Accordingly, there is a need for a nacelle for a turbofan jet engine having an inlet assembly that addresses the foregoing and other related and unrelated problems in the art.